1. Field of the Invention
The present invention relates to the gallium-nitride (GaN) based light emitting diode (LED), and in particular to the structure of the light-emitting layer of the GaN-based LED.
2. The Prior Arts
LEDs have long been widely used as indicators or light sources in various electronic consumer devices due to their features including low power consumption, low heat dissipation, and long operation life. In recent years, researches have been focused on the development of LEDs with various colors and LEDs with high luminance. Among these researches, highly efficient and illuminant blue-light LEDs that can be put to practical use receive the most attention. In October 1995, Nichia Corporation, Japan, announced the successful production of highly illuminant blue-light LEDs based on the indium-gallium-nitride (InGaN) material. This breakthrough has led the world's optoelectronic industry to invest tremendous capitals and resources in the gallium-nitride (GaN) based, such as GaN, aluminum-gallium-nitride (AlGaN), indium-gallium-nitride (InGaN), etc., LEDs.
FIG. 1 is a schematic diagram showing the structure of a GaN-based LED according to prior arts. As shown in FIG. 1, the conventional structure of a GaN-based LED contains a substrate 10 made of sapphire. Then, on one side of the sapphire substrate 10, the GaN-based LED further contains an n-type GaN contact layer 11, an InGaN light-emitting layer 12, and a p-type GaN contact layer 13, sequentially stacked from bottom to top in this order. In addition, there are a positive electrode 14 and a negative electrode 15 stacked upon the p-type GaN contact layer 13 and the n-type GaN contact layer 11 respectively. Within this conventional GaN-based LED structure, the light-emitting layer 12 usually has a multi-quantum well (MQW) structure made of InxGa1-xN (0≦x≦1). The electrons and holes are joined with each other within the InxGa1-xN (0≦x≦1) potential well and photons are thereby released. Please note that the epitaxial growth of the InxGa1-xN (0≦x≦1) requires a very high temperature to obtain epitaxial layer with better quality. On the other hand, to increase the possibility of forming the electron-hole pairs and thereby the lighting efficiency, the growing temperature of the InxGa1-xN (0≦x≦1) cannot be higher than 850° C. so that multiple localized states can be formed from the characteristics of the InxGa1-xN (0≦x≦1) such as indium segregation and phase separation. This is a dilemma requiring an appropriate solution.